<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<script>


    //定义一个学生的类
    class Student{

        constructor(name) {
            this.name = name;
        }

        hello(){
            alert("hello!")
        }
    }

    class XiaoStudent extends Student{

        constructor(name,grade){
            super(name);
            this.grade = grade;
        }

        hello() {
            alert("我是一名小学生！")
        }
    }

    var xiaoming = new Student("xiaoming");
    var xiaohong = new Student("xiaohong");

    var xiaozhi = new XiaoStudent("xiaozhi",1);

</script>
</body>
</html>